Wafer level packaging structure with large contact area and preparation method thereof

ABSTRACT

A method to provide a wafer level package with increasing contact pad area comprising the steps of forming a first packaging layer on wafer top surface, grinding the wafer back surface and etch through holes, depositing a metal to fill the through holes and covering wafer backside, cutting through the wafer from wafer backside forming a plurality of grooves separating each chip then depositing a second packaging layer filling the grooves and covering the wafer back metal, reducing the first packaging layer thickness to expose the second packaging layer filling the grooves and forming a plurality of contact pads overlaying the first packaging layer thereafter cutting through the second packaging layer in the grooves to form individual package.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/205,864, filed on Aug. 9, 2011, which application isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention generally relates to a wafer level packaging structure,particularly, to a wafer level packaging structure with a larger contactarea and a preparation method thereof.

DESCRIPTION OF THE RELATED ART

Wafer level chip scale package (WLCSP) refers to the technology ofpackaging an integrated circuit (IC) at the wafer level, which comprisesthe following steps: after finishing the formation of semiconductorchips on a whole wafer, a packaging test is directly performed on thewafer and solder balls or solder bumps are formed; then single IC(Integrated Circuit) packages are singulated, where the resulting ICpackage is of the same size of the chip. The solder balls or solderbumps formed on wafer level chips are used as a contact terminal forelectrically connecting the chip to an external circuit. It is wellknown that the power consumption of a power device is very high.Usually, the solder balls or the solder bumps are directly formed on abonding pad of a Printed Circuit Board (PCB) and the volume of thesolder balls or the solder bumps is small, thus the contact area of thesolder balls or the solder bumps is limited, which results in highimpedance and low thermal conductance effects. In addition, the chip isexposed because of lacking in physical protection, thus the chip iseasily damaged in treatment and is highly vulnerable to moisture.

The US publication number 2009/0032871 discloses an integrated circuitincluding an active area, a first metal contact at a front surface ofthe active area and a second metal contact at a back surface of theactive area, and a wafer-level deposited metal structure positionedadjacent to an edge of the active area for interconnecting the first andsecond metal contact. As shown in FIG. 1A, the semiconductor wafer 190includes two semiconductor chips 200 a and 200 b that can be singulatedthrough a groove 202. Each of the chips 200 a and 200 b includes frontside metal contacts 104 a, 104 b and 104 c arranged on its front surfaceand a metal interconnection 110 located at the sidewall of the groove202 and connected to the front side metal contact 104 c. In FIG. 1B,thinned chips 151 a, 151 b and 151 c are singulated. Each chip 151 a,151 b and 151 c includes front side metal contacts 104 arranged at thefront surface of the active area and a backside metal contact arrangedat the backside of the active area with the front side metal contact 104c connected to the backside metal contact 108 through the metalinterconnection 110. The back side metal contact 108 forms an electrodeat the bottom of the chip. Each chip 151 a, 151 b and 151 c alsoincludes packaging material 102 and a plurality of solder balls 152formed on the front side metal contacts 104 a, 104 b and 104 c, whichare used for electrically connecting the chips 151 a, 151 b and 151 c tothe outside circuit. However, when the solder balls 152 are connected onthe bonding pad on the PCB, the contact area between the solder balls152 and the bonding pad on the PCB is very small, thus it is results innegative effects of high impedance and low thermal conduction when thechips 151 a, 151 b and 151 c are applied in a power device.

BRIEF DESCRIPTION OF THE DRAWINGS

As shown in attached drawings, the embodiment of the invention is moresufficiently described. However, the attached drawings are only used forexplaining and illustrating rather than limiting the scope of theinvention.

FIGS. 1A-1B are cross-sectional views of an integrated circuit of theprior art.

FIGS. 2A-2M are schematic diagrams illustrating a wafer level packagingmanufacturing process according to a first embodiment of the presentinvention.

FIGS. 3A-3D are schematic diagrams illustrating a wafer level packagingmanufacturing process according to a second embodiment of the presentinvention.

FIGS. 4A-4J are schematic diagrams illustrating a water level packagingmanufacturing process according to a third embodiment of the presentinvention.

FIGS. 5A-5C are schematic diagrams illustrating a wafer level packagingmanufacturing process according to a fourth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 2A, a wafer 200 generally includes a plurality ofsemiconductor chips with a scribe line used for defining the boundarybetween the adjacent chips (not shown), so that the individual chips canbe singulated from the wafer 200 along the scribe line. It is well knownin the art that, after finishing the manufacturing process of the wafer200 to form the semiconductor chips, a plurality of first metal bondingpads 201 and 202 are formed at the front surface of wafer 200,particularly, at the front surface of each chip. The first metal bondingpads 201 and 202 can be aluminum silicon metal pad (I/O pad)pre-designed on the chip and are used as electrodes of the chips orterminals in signal transmission with the outside circuit.

Furthermore, a second metal bonding pad 203 is formed at the frontsurface of each chip, which can be made of metal materials such asaluminum-silicon alloy and the likes. For the sake of simplicity, apassivation layer for separating the first metal bonding pads 201 and202 from the second metal bonding pad 203 is not shown in the figures.The first metal bonding pads 201 and 202 are electrically connected tothe integrated circuit inside the chip, while the second metal bondingpad 203 is not electrically connected to the integrated circuit insidethe chip.

Referring to FIG. 2B, a first packaging layer 210 is formed to cover thefront surface of wafer 200, the first metal bonding pads 201 and 201 andthe second metal bonding pad 203. Then, the back surface of the wafer200 is ground (for example, chemical mechanical polishing) to reduce itsthickness, as shown in FIG. 2C. As the first packaging layer 210 caneffectively physically support for the wafer 200, the thickness of wafer200 can be thinned enough without being cracked, as such the thicknessof the chip formed in the wafer 200 is also thinned. Optionally, afterthe wafer 200 is thinned, the back surface of the wafer 200 is heavilydoped with ions. Then, the wafer 200 is etched from its back surface toform a bottom through hole 204, as shown in FIG. 2D. In particular, thebottom through hole 204 is formed in each chip formed in the wafer 200,in which, the second metal bonding pad 203 is in superimposition withthe bottom through hole 204 with the bottom through hole 204 extendingto the front surface of the chip exposing the second metal bonding pad203. The existing TSV (Through Silicon Via) technology, dry etching, wetetching or laser etching is suitable for the etching step for formingthe bottom through hole 204. It is generally required that thecross-sectional area of the bottom through hole 204 is smaller than thecontact area of the second metal bonding pad 203. After the bottomthrough hole 204 is formed, an insulation layer (not shown), such asSiO₂ and the like, is deposited at the side wall of the bottom throughhole 204. However, since the bottom through hole 204 occupies a certainspace of the chip, the bottom through hole 204 is formed in anon-effective circuit area in order to minimize the possible negativeeffects, i.e., the bottom through hole 204 is not formed in an effectiveintegrated circuit unit in the chip or the etched area is formed in acircuit blank area. As such, even the bottom through hole 204 is formedin the chip, there is no adverse effect on the original circuit of thechip.

As shown in FIG. 2E, a conductive material is filled in the bottomthrough hole 204 forming a bottom metal interconnecting structure 204 aconnected to the second metal bonding pad 203. The bottom metalinterconnecting structure 204 a is electrically insulated from theconductive material of the chip surrounding the bottom through hole 204through the insulation layer covering the side wall of the bottomthrough hole 204 as described above. Then, a metal layer 211 isdeposited to cover the back surface of the wafer 200, which iselectrically connected to the bottom metal interconnecting structure 204b. As such the metal layer 211 is electrically connected to the metalbonding pad 203 through the bottom metal interconnecting structure 204a.

As shown in FIG. 2F, the wafer 200 and the metal layer 211 are cut fromthe back surface of the wafer 200 along the scribe line on the wafer 200to form a plurality of cutting grooves 205 extending into the firstpackaging layer 210. As such, individual chips 200′ formed in the wafer200 are separated by the cutting grooves 205. At the same time, themetal layer 211 is cut into a plurality of bottom metal layers 211′,each of which is formed at the back surface of each chip 200′. Thus, thebottom metal layer 211′ is electrically connected to the second metalbonding pad 203 positioned at the front surface of the chip 200′ throughthe bottom metal interconnecting structure 204 a. The ions doped at theback surface of the wafer 200 or at the back surface of the chip 200′providing a good ohmic contact between the back surface of the chip 200′and the bottom metal layer 211′.

As shown in FIG. 2G, a packaging material is deposited to form a secondpackaging layer 212 to cover bottom metal layers 211′ and to fill intothe cutting groove 205 as well. As shown in FIG. 2H, the packaging bodyis preferred to be as thin and compact as possible, therefore the firstpackaging layer 210 is thinned until the packaging material 212 filledin the cutting groove 205 is exposed and a plurality of top packaginglayers 210′ are formed, each of which covers the front surface of eachchip 200′, with adjacent top packaging layers 210′ separated bypackaging material 212 filled in the cutting groove 205.

As shown in FIG. 2I, the top packaging layer 210′ is etched (forexample, laser etching) to expose the first metal bonding pads 201 and202 and the second metal bonding pad 203, thus forming a plurality oftop through holes 206, 207 and 208 at the first metal bonding pads 201and 202 and the second metal bonding pad 203 respectively. Inparticular, the top through hole 206 is aligned with the first metalbonding pad 201, the top through hole 207 is aligned with the firstmetal bonding pad 202, and the top through hole 208 is aligned with thesecond metal bonding pad 203. As shown in FIG. 2J, the conductivematerial is filled into through holes 206, 207 and 208 forming the topmetal interconnecting structure 206 a connected to the first metalbonding pad 201, a top metal interconnecting structure 207 a connectedto the first metal bonding pad 202 and a top metal interconnectingstructure 208 a connected to the second metal bonding pad 203.Hereafter, a plurality of contact bonding pads 221, 222 and 223 areformed on the top packaging layer 210′ and are electrically connected tothe first metal bonding pad 201, the first metal bonding pad 202 and thesecond metal bonding pad 203 respectively through the top metalinterconnecting structure 206 a, the top metal interconnecting structure207 a and the top metal interconnecting structure 208 a respectively.

As shown in FIG. 2K, individual wafer level packaging structures 250 areseparated from each other by cutting the second packaging layer 212 andthe packaging material filled in the cutting groove 205 along thecutting groove 205 forming a cutting groove 215. If a width of thecutting groove 215 is narrower than that of the cutting groove 205, theremaining of the packaging material filled into the cutting groove 205,after being cut, forms a side packaging layer 212 b covering the sidesurface of the chip 200′. Each wafer level packaging structure 250includes the first metal bonding pads 201 and 202 and the second metalbonding pad 203 formed at the front surface of the chip 200′, and abottom metal layer 211′ covering the back surface of the chip 200′. Thesecond metal bonding pad 203 is positioned above a bottom through hole204, which is extends from the front surface to the back surface of thechip 200′, and is electrically connected to the bottom metal layer 211′through the bottom metal interconnecting structure 204 a formed in thebottom through hole 204, which is electrically insulated from theconductive material of the chip 200′ surrounding the bottom through hole204 by the insulation layer (not shown) formed on the side wall of thebottom through hole 204. The wafer level packaging structure 250 furtherincludes the top packaging layer 210′ covering the front surface of thechip 200′, the bottom packaging layer 212 a covering the bottom metallayer 211′ and a side packaging layer 212 b covering the side surface ofchip 200′. The wafer level packaging structure 250 further includes aplurality of contact bonding pads 221, 222 and 223 formed atop the toppackaging layer 210′, which are electrically connected to the firstmetal bonding pad 201, the first metal bonding pad 202 and the secondmetal bonding pad 203 through top metal interconnecting structures 206a, 207 a and 208 a respectively. The area of each contact bonding padmay be maximized by extending each contact bonding pad to the twoadjacent edges of the top packaging layer 210′ having an increased arealarger than the corresponding top metal interconnecting structure andthe first or second metal bonding pad.

In an embodiment mode, the chip 200′ is a vertical power semiconductordevice, for example, a vertical metal oxide semiconductor field effecttransistor (MOSFET). In this case, the first metal bonding pad 201 is agate electrode of the chip 200′, the first metal bonding pad 202 is asource electrode of the chip 200′ and a drain area of the MOSFET isformed at the back surface of the chip 200′. The drain electrode of thechip 200′ is formed on the bottom metal layer 211′, therefore the drainelectrode of the chip 200′ is electrically connected to the second metalbonding pad 203 positioned at the front surface of the chip 200′ throughthe bottom metal interconnecting structure 204 a as described above. Thecontact bonding pad 221 electrically connected with the first metalbonding pad 201 is functioned as an external gate terminal of the chip200′. The contact bonding pad 222 electrically connected with the firstmetal bonding pad 202 is functioned as an external source terminal ofthe chip 200′, and the contact bonding pad 223 electrically connectedwith the second metal bonding pad 203 is functioned as an external drainterminal of the chip 200′. The contact bonding pads 221, 222 and 223 canbe directly connected to a bonding pad (generally plating tin on thesurface) preset on the PCB. Larger size of contact bonding pads 221, 222and 223 are, larger contact area of the contact bonding pads 221, 222and 223 and the bonding pads on the PCB is achieved, thus the impedanceand the thermal conduction effect is improved when the chip 200′ iselectrically connected with the external circuit. The top packaginglayer 210′, the bottom packaging layer 212 a and the side packaginglayer 212 b of the chip 200′ improve the mechanical strength of the chip200′ and protect the chip 200′ from moisture or other adverseenvironmental factors. The wafer level package structure 250 of thepresent invention is very thin without using of any lead-frame, soldermaterial (such as conductive silver paste and the like) as a binder forconnecting the chip, and bonding wire that may cause negative highimpedance effect for electrical connection.

The contact bonding pads 221, 222 and 223 may be formed by metaldeposition on the top packaging layer 210′ using a mask (not shown).Particularly, a metal layer may be firstly deposited on the toppackaging layer 210′. The mask is applied atop of the metal layer, thusthe metal layer is etched through the openings on the mask forming thecontact bonding pads 221, 222 and 223. In addition, for two contactbonding pads positioned at the edge of the adjacent chips, for exampleas shown in FIG. 2J contact bonding pads 223 of a first chip 200′ (leftside of FIG. 2J) and contact bonding pad 221 of a second chip 200′(right side of FIG. 2J), contact bonding pads 223 and 221 may be formedby firstly forming one common bonding pad positioned above the cuttinggroove 205 filled with packaging material, then the contact bonding pad223 and the contact boding pad 221 are separated when the packagingmaterial filled in the cutting groove 205 and the second packaging layer212 are cut through (FIG. 2K).

FIG. 2L is a top view of the wafer level packaging structure 250.Compared with the existing packaging structure (FIG. 1B), the contactarea for electrically connecting to an external circuit of the solderball 152 is small due to small volume of the solder ball 152, in thepackaging structure 250 of the present invention, the contact bondingpads 221, 222 and 223 provides larger contact area for electricalconnecting to the external circuit. The shape of the contact bondingpads 221, 222 and 223 can be selected depending on the application ofthe device; for example, as shown in FIG. 2M, the contact pads 222 and223 can be shaped with a plurality of pins 222′ and 223′ respectively.Obviously, in the wafer level packaging structure 250 shown in FIG. 2M,the contact bonding pads 221, 222 and 223 with the pins 222′ and 223′extending to the edge of the chip 200′ can be compatible withtraditional Quad Flat No-lead (QFN) Package, so that this packagingstructure can be mounted on any PCB suitable for soldering the packagingbody such as the QFN and the like through a surface mount technology(SMT).

In another preferred embodiment, the packaging structure, as shown inFIG. 2E, can be obtained via the process as shown in FIGS. 3A-3D. In aninitial state, a plurality of first metal bonding pads 201 and 202 areoriginally formed at the front surface of the chip formed in the wafer200 as shown in FIG. 3A. Etching is carried out at the front surface ofthe chip to form a bottom through hole 204 in each chip formed in thewafer 200. The bottom through hole 204 extends downwards from the frontsurface of the chip to a certain depth but not penetrating through thewhole thickness of the wafer 200. Then the bottom through hole 204 isfilled with the conductive material forming the bottom metalinterconnecting structure 204 a. As mentioned above, the bottom throughhole 204 is formed in a non-effective circuit preparing area of thechip. An insulation layer (for example SiO₂) (not shown) is deposited tocover the side wall of the bottom through hole 204 before filing thethrough hole 204 with conductive material to form the bottom metalinterconnecting structure 204 a, as such the bottom metalinterconnecting structure 204 a is electrically insulated from theconductive material of the chip surrounding the bottom through hole 204through the insulation layer. As shown in FIG. 3B, one second metalbonding pad 203 is formed at the front surface of the chip formed in thewafer 200, which is in superimposition and electrically connected to thebottom metal interconnecting structure 204 a. As shown in FIG. 3C, thefirst packaging layer 210 is formed to cover the front surface of thewafer 200, the first metal bonding pads 201 and 202 and the second metalbonding pad 203. The wafer 200 is thinned by grinding from its backsurface physically supporting by the first packaging layer 210 until thebottom metal interconnecting structure 204 a is exposed at the backsurface of the wafer 200 and the designed wafer thickness is obtained.The back surface of the thinned wafer 200 is then heavily doped withions followed by the deposition of the metal layer 211 at the backsurface of the wafer 200. The metal layer 211 is connected to the bottommetal interconnecting structure 204 a (as shown in FIG. 2E). Thecomplete wafer level package structure 250 is then formed with the stepsdescribed in FIGS. 2E-2M.

Another method for preparing wafer level packaging structures of thepresent invention is shown in FIGS. 4A-4J. In the initial state, aplurality of first metal bonding pads 201 and 202 are originally formedat the front surface of the chip formed in the wafer 200. In thisembodiment, one second metal bonding pad 203 is form at the frontsurface of each chip. Then a plurality of top metal interconnectingstructures 206′a, 207′a and 208′a are respectively formed on the firstmetal bonding pad 201, the first metal bonding pad 202 and the secondmetal bonding pad 203 correspondingly. The top metal interconnectingstructures 206′a, 207′a and 208′a can be made of conductive materialssuch as solder balls or solder bumps and the likes. As shown in FIG. 4B,the first packaging layer 210 is formed to cover the front surface ofthe wafer 200, the first metal bonding pad 201, the first metal bondingpad 202, the second metal bonding pad 203 and the top metalinterconnecting structures 206′a, 207′a and 208′a. As shown in FIG. 4C,the back surface of the wafer 200 is ground to reduce the thickness ofthe wafer 200. As shown in FIG. 4D, each chip of the thinned wafer 200is etched from its back surface to form one bottom through hole 204beneath the second metal bonding pad 203. After the bottom through hole204 is formed, an insulation layer is deposited on the side wall of thebottom through hole 204. The bottom through hole 204 is then filled withthe conductive material to form the metal interconnecting structure 204a. As mentioned above, the bottom through hole 204 is formed in thenon-effective circuit preparing area of the chip. Thus, the bottom metalinterconnecting structure 204 a is connected to the second metal bondingpad 203. As shown in FIG. 4E, firstly, the back surface of the thinnedwafer 200 is heavily doped with ions, then a metal layer 211 isdeposited at the back surface of the wafer 200. As shown in FIG. 4F, thewafer 200 and the metal layer 211 are cut from the back surface, forminga plurality of cutting grooves 205. The depth of the cutting groove 205can be varied, for example, the cutting grooves 205 can extend into thefirst packaging layer 210 as shown in FIG. 4F. As such, individual chips200′ formed in the wafer 200 are separated from each other by thecutting groove 205 and the metal layer 211 is also cut into a pluralityof bottom metal layers 211′, each of which is formed at the back surfaceof each chip 200′.

As shown in FIG. 4G, a packaging material is deposited to form a secondpackaging layer 212 at the back surface of the wafer 200 to cover bottommetal layers 211′ and to fill into the cutting groove 205. As shown inFIG. 4H, the first packaging layer 210 is thinned until the packagingmaterials filled in the cutting groove 205 and the top metalinterconnecting structures 206′a, 207′a and 208′a are exposed forming aplurality of top packaging layers 210′ separated by the packagingmaterials filled in the cutting groove 205, with each of the toppackaging layers 210′ covering the front surface of each chip 200′. Asshown in FIG. 4I, a plurality of contact bonding pads 221, 222 and 223are formed atop the top packaging layer 210′, each of which iselectrically connected to one of first metal bonding pads 201 and 202 orone second metal bonding pad 203 correspondingly through one top metalinterconnecting structure. As shown in the figure, the contact bondingpad 221 is formed on the top metal interconnecting structure 206′a andis electrically connected to the first metal bonding pad 201 through thetop metal interconnecting structure 206′a. The contact bonding pad 222is formed on the top metal interconnecting structure 207′a and iselectrically connected to the first metal bonding pad 202correspondingly through the top metal interconnecting structure 207′a.The contact bonding pad 223 is formed on the top metal interconnectingstructure 208′a and is electrically connected to the second metalbonding pad 203 through the top metal interconnecting structure 208′a.As shown in FIG. 4J, the individual wafer level packaging structures250′ are separated from each other by cutting through the secondpackaging layer 212 and the packaging materials filled in the cuttinggroove 205 forming the cutting groove 215. As such, the second packaginglayer 212 is cut into a plurality of the bottom plastic packaging layers212 a, each of which covers the bottom metal layer 211′ of the packagestructure 250′. If the width of the cutting groove 215 is narrower thanthat of the cutting groove 205, the remaining of packaging materialsfilled in the cutting groove 205 forms the side packaging layer 212 bcovering the side of the chip 200′.

In another embodiment, as shown in FIGS. 5A-5C, the process is startedwith the structure as shown in FIG. 3B. Then, as shown in FIG. 5A, thetop metal interconnecting structures 206′a, 207′a and 208′a is formed onthe first metal bonding pad 201, the first metal bonding pad 202 and thesecond metal bonding pad 203. The top metal interconnecting structure206′a, 207′a and 208′a can be made of solder tin balls or metal bumps orother materials. As shown in FIG. 5B, the first packaging layer 210 isformed to cover the front surface of the wafer 200, the first s metalbonding pads 201 and 202, the second metal bonding pad 203 and the topmetal interconnecting structure 206′a, 207′a and 208′a. As shown in FIG.5C, the back surface of the wafer 200 is ground until the bottom metalinterconnecting structure 204 a is exposed at the back surface of thewafer 200 and the predetermined thickness of the wafer is obtained. Theback surface of the thinned wafer 200 is then heavily doped with ionsfollowed by the formation of a metal layer 211 covering the back surfaceof the wafer 200. As such, the metal layer 211 is connected to thebottom metal interconnecting structure 204 a. The structure of FIG. 5Cis equivalent with the structure of FIG. 4E before forming the bottommetal layer 211. The complete wafer level package structure 250′ is thenformed with the steps described in FIGS. 4E-4J.

Hereinbefore, through descriptions and drawings, the typical embodimentsof the specific structures of the specific embodiment modes areprovided, and the existing preferable embodiments are provided in theinvention, however, these contents are not used as the limit. For thetechnical personnel of the field, all changes and amendments areundoubtedly obvious after reading the above specification. Consequently,the attached claims should be regarded as all changes and amendmentsconvering the real intention and the scope of the invention. In thescope of the claims, any and all equivalent scopes and contents shouldbe considered still belonging to the intention and the scope of theinvention.

1. A method for preparing a wafer level packaging structure with largecontact area, wherein a plurality of first metal bonding pads are formedat a front surface of semiconductor chips formed in a semiconductorwafer, comprising the following steps: forming at least a second metalbonding pad at the front surface of each chip; forming a first packaginglayer covering the first metal bonding pads and the second metal bondingpads and the front surface of the wafer; etching from a back surface ofthe wafer to form a bottom through hole to expose the second metalbonding pad in the chip and filling a conductive material in the bottomthrough hole to form a bottom metal interconnecting structure connectedto the second metal bonding pad; forming a metal layer covering the backsurface of the wafer connected to the bottom metal interconnectingstructure; cutting through the wafer and the metal layer from the backsurface of the wafer to form a plurality of cutting grooves, wherein thecutting grooves extend into the first packaging layer and separateindividual chips from each other, and wherein the metal layer is cutinto a plurality of bottom metal layers, each of which covers the backsurface of each chip; depositing a packaging material to form a secondpackaging layer covering the bottom metal layers and to fill into thecutting groove; thinning the first packaging layer until the packagingmaterial filled in the cutting groove being exposed, whereby forming aplurality of top packaging layers, each of which covers the frontsurface of each chip; etching the top packaging layer to expose thefirst metal bonding pads and the second metal bonding pad thus forming aplurality of top through holes above the first metal bonding pads andthe second metal bonding pad and filing a conductive material into thetop through holes to form a plurality of top metal interconnectingstructures connected to the first metal bonding pads and the secondmetal bonding pad respectively; forming a plurality of contact bondingpads atop the top plastic packaging layer, wherein one contact bondingpad is electrically connected to one first metal bonding pad or onesecond metal bonding pad through at least one top metal interconnectingstructure; and cutting through the second packaging layer and thepackaging material filled in the cutting groove along the cutting grooveto separate individual wafer level packaging structures from each other,wherein the second packaging layer is cut into a plurality of bottompackaging layers, each of which covers the bottom metal layer of eachchip.
 2. The method of claim 1, wherein the back surface of the wafer isthinned before forming the bottom through hole.
 3. The method of claim1, wherein after the bottom through hole is formed, an insulation layeris deposited to cover the side wall of the bottom through hole beforefilling the bottom through hole with the conductive material to form thebottom metal interconnecting structure, therefore the bottom metalinterconnecting structure is electrically insulated from conductivematerial of the chip surrounding the bottom through hole through theinsulation layer.
 4. The method of claim 1, wherein the back surface ofthe wafer is heavily doped with ions before the metal layer is formed atthe back surface of the wafer.
 5. The method of claim 1, wherein thebottom through hole is formed in a non-effective circuit preparing areaof the chip.
 6. The method of claim 1, wherein the semiconductor chip isa MOSFET (Metal Oxide Semiconductor Field Effect Transistor), in whichthe plurality of first metal bonding pads comprise a gate electrode anda source electrode of the chip, and a drain electrode of the chip isformed at the bottom metal layer.
 7. The method of claim 1, wherein theremaining of the packaging material filled in the cutting groove, aftercutting through the second plastic packaging layer and the plasticpackaging material filled in the cutting groove along the cuttinggroove, forms a side packaging layer covering the side surface of thechip.
 8. The method of claim 1, wherein the bottom through hole isformed by dry etching, wet etching or laser etching.
 9. The method ofclaim 1, wherein the plurality of top through holes are formed by laseretching in the top packaging layer.
 10. A method for preparing a waferlevel packaging structure with large contact area, wherein a pluralityof first metal bonding pads are formed at a front surface ofsemiconductor chips formed in a semiconductor wafer, comprising thefollowing steps: etching at the front surface of each chip to form atleast a bottom through hole with the depth shorter than the thickness ofthe wafer and filling a conductive material in the bottom through holeto form a bottom metal interconnecting structure; forming at least asecond metal bonding pad at the front surface of the chip and above thebottom metal interconnecting structure, the second metal bonding pad iselectrically connected to the bottom metal interconnecting structure;forming a first packaging layer covering the first metal bonding padsand the second metal bonding pads and the front surface of the wafer;grinding the back surface of the wafer until the bottom metalinterconnecting structure exposed at the back surface of the wafer;forming a metal layer covering the back surface of the wafer connectedto the bottom metal interconnecting structure; cutting through the waferand the metal layer from the back surface of the wafer to form aplurality of cutting grooves, wherein the cutting groove extends intothe first packaging layer and separates individual chips from eachother, and wherein the metal layer is cut into a plurality of bottommetal layers, each of which covers the back surface of each chip;depositing a packaging material to form a second packaging layercovering the bottom metal layer and to fill into the cutting groove;grinding the first packaging layer until the packaging material filledin the cutting groove is exposed, wherein the first packaging layer iscut into a plurality of top packaging layers, each of which covers thefront surface of each chip; etching the top packaging layer to exposethe first metal bonding pads and the second metal bonding pad thusforming a plurality of top through holes above the first metal bondingpads and the second metal bonding pad, and filling a conductive materialinto the top through holes to form a plurality of top metalinterconnecting structures connected to the first metal bonding pads andthe second metal bonding pad respectively; forming a plurality ofcontact bonding pads atop the top plastic packaging layer, wherein eachcontact bonding pad is electrically connected to one first metal bondingpad or one second metal bonding pad through at least one top metalinterconnecting structure; and cutting through the second packaginglayer and the packaging material filled in the cutting groove along thecutting groove to separate individual wafer level packaging structuresfrom each other, wherein the second packaging layer is cut into aplurality of bottom packaging layers, each of which covers the bottommetal layer of each chip.
 11. The method of claim 10, wherein after thebottom through hole is formed, an insulation layer is deposited to coverthe side wall of the bottom through hole before filing the conductivematerial into the bottom through hole to form the bottom metalinterconnecting structure, therefore the bottom metal interconnectingstructure is electrically insulated from conductive material of the chipsurrounding the bottom through hole through the insulation layer. 12.The method of claim 10, wherein the back surface of the wafer is heavilydoped with ions before the metal layer is formed at the back surface ofthe wafer.
 13. The method of claim 10, wherein the bottom through holeis formed in a non-effective circuit preparing area of the chip.
 14. Themethod of claim 10, wherein the semiconductor chip is a MOSFET (MetalOxide Semiconductor Field Effect Transistor), wherein the plurality offirst metal bonding pads comprise a gate electrode and a sourceelectrode of the chip, and a drain electrode of the chip is formed atthe bottom metal layer.
 15. The method of claim 10, wherein theremaining of the packaging material filled in the cutting groove, aftercutting through the second plastic packaging layer and the plasticpackaging material filled in the cutting groove along the cuttinggroove, forms a side packaging layer covering the side of the chip. 16.A method for preparing a wafer level packaging structure with largecontact area, wherein a plurality of first metal bonding pads are formedat a front surface of semiconductor chips formed in a semiconductorwafer, comprising the following steps: forming at least a second metalbonding pad at the front surface of the chip; forming a plurality of topmetal interconnecting structures on the first metal bonding pads and thesecond metal bonding pad; forming a first packaging layer covering thefirst metal bonding pads, the second metal bonding pad, the top metalinterconnecting structures and the front surface of the wafer; etchingthe back surface of the wafer to form a bottom through hole to exposethe second metal bonding pad and filling a conductive material in thebottom through hole to form a bottom metal interconnecting structureconnected to the second metal bonding pad; forming a metal layercovering the back surface of the wafer connected to the bottom metalinterconnecting structure; cutting through the wafer and the metal layerfrom the back surface of the wafer to form a plurality of cuttinggrooves extending into the first packaging layer and separatingindividual chips from each other, wherein the metal layer is cut into aplurality of bottom metal layers each of which is formed of at the backsurface of each chip; depositing a packaging material to form a secondpackaging layer covering the bottom metal layer and to fill into thecutting groove; grinding the first packaging layer until exposing thepackaging material filled in the cutting groove and the top metalinterconnecting structures, wherein the first packaging layer is cutinto a plurality of top packaging layers each of which covers the frontsurface of each chip; forming a plurality of contact bonding pads atopthe top packaging layer, wherein each contact bonding pad iselectrically connect to one first metal bonding pad or one second metalbonding pad through at least one top metal interconnecting structure;and cutting through the second packaging layer and the packagingmaterial filled in the cutting groove along the cutting groove toseparate individual wafer level packaging structures from each other,wherein the second packaging layer is cut into a plurality of bottompackaging layers each of which covers the bottom metal layer of eachchip.
 17. The method of claim 16, wherein the top metal interconnectingstructure is a solder tin ball or a metal bump.
 18. The method of claim16, wherein the wafer is ground at the back surface to thin the waferbefore the bottom through hole is formed.
 19. The method of claim 16,wherein after the bottom through hole is formed, an insulation layer isdeposited to cover the side wall of the bottom through hole before theconductive material is filled in the bottom through hole to form thebottom metal interconnecting structure, therefore the bottom metalinterconnecting structure is electrically insulated from conductivematerial of the chip surrounding the bottom through hole through theinsulation layer.
 20. The method of claim 16, wherein the back surfaceof the wafer is heavily doped with ions before the metal layer is formedat the back surface of the wafer.
 21. The method of claim 16, whereinthe bottom through hole is formed in a non-effective circuit preparingarea of the chip.
 22. The method of claim 16, wherein the semiconductorchip is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor),wherein the plurality of first metal bonding pads comprise a gateelectrode and a source electrode of the chip, and a drain electrode ofthe chip is formed at the bottom metal layer.
 23. The method of claim16, wherein the remaining of the packaging material filled in thecutting groove, after cutting through the second plastic packaging layerand the plastic packaging material filled in the cutting groove alongthe cutting groove, forms a side packaging layer covering a side surfaceof the chip.
 24. A method for preparing a wafer level packagingstructure with large contact area, where a plurality of first metalbonding pads are formed at a front surface of semiconductor chips formedin a wafer, comprising the following steps: etching from the frontsurface of each chip to form at least a bottom through hole with thedepth shorter than the thickness of the wafer and filling a conductivematerial into the bottom through hole to form a bottom metalinterconnecting structure; forming at least a second metal bonding padat the front surface of the chip connected to the bottom metalinterconnecting structure; forming a plurality of top metalinterconnecting structures on the first metal bonding pads and thesecond metal bonding pad; forming a first packaging layer covering thefirst metal bonding pads, the second metal bonding pads, the top metalinterconnecting structures and the front surface of the wafer; thinningthe back surface of the wafer until exposing the bottom metalinterconnecting structure; forming a metal layer covering the backsurface of the wafer connected to the bottom metal interconnectingstructure; cutting through the wafer and the metal layer from the backsurface of the wafer to form a plurality of cutting grooves extendinginto the first packaging layer and separating the individual chips fromeach other, wherein the metal layer is cut into a plurality bottom metallayers each of which is formed at the back surface of each chip;depositing a packaging material to form a second packaging layercovering the bottom metal layer and to fill into the cutting groove;grinding to thin the first packaging layer until exposing the plasticpackaging material filled in the cutting groove and the top metalinterconnecting structure, wherein the first packaging layer is cut intoa plurality of top packaging layers each of which is formed at the frontsurface of each chip; forming a plurality of contact bonding pads on thetop packaging layer, each of which is electrically connected to onefirst metal bonding pad or one second metal bonding pad through at leastone top metal interconnecting structure; and cutting through the secondpackaging layer and the packaging material filled in the cutting groovealong the cutting groove to separate individual wafer level packagingstructures from each other, wherein the second packaging layer is cutinto a plurality of bottom packaging layers each of which covers thebottom metal layer of each chip.
 25. The method of claim 24, wherein thetop metal interconnecting structure is a solder tin ball or a metalbump.
 26. The method of claim 24, wherein after the bottom through holeis formed, an insulation layer is deposited to cover the side wall ofthe bottom through hole before the conductive material is filled intothe bottom through hole to form the bottom metal interconnectingstructure, therefore the bottom metal interconnecting structure iselectrically insulated from conductive material of the chip surroundingthe bottom through hole through the insulation layer.
 27. The method ofclaim 24, wherein the back surface of the wafer is heavily doped withions before the metal layer is formed at the back surface of the wafer.28. The method of claim 24, wherein the bottom through hole is formed ina non-effective circuit preparing area.
 29. The method of claim 24,wherein the semiconductor chip is a MOSFET (Metal Oxide SemiconductorField Effect Transistor), wherein the plurality of first metal bondingpads comprise a gate electrode and a source electrode of the chip, and adrain electrode of the chip is formed at the bottom metal layer.
 30. Themethod of claim 24, wherein the remaining of the packaging materialfilled in the cutting groove, after cutting through the second plasticpackaging layer and the plastic packaging material filled in the cuttinggroove along the cutting groove, forms a side packaging layer covering aside surface of the chip.
 31. A wafer level packaging structure withlarge contact area, comprising: a plurality of first metal bonding padsand a second metal bonding pad formed at a front surface of asemiconductor chip; a bottom metal layer covering a back surface of thesemiconductor chip; a bottom through hole formed in the chip beneath thesecond metal bonding pad extending from the front surface of the chip tothe back surface of the chip, wherein the bottom through hole is filledwith a conductive material forming a bottom metal interconnectingstructure, therefore the bottom metal layer is electrically connected tothe second metal bonding pad through the bottom metal interconnectingstructure; a top packaging layer covered the front surface of thesemiconductor chip; a bottom packaging layer covered the bottom metallayer; a plurality of top metal interconnecting structures formed on andelectrically connected to the first metal bonding pads and the secondmetal bonding pad; and a plurality of contact bonding pads formed atopthe top plastic packaging layer, wherein one of the plurality contactbonding pads is correspondingly electrically connected to one of theplurality of first metal bonding pads or the second class metal bondingpad through at least one of the plurality of top metal interconnectingstructures.
 32. The wafer level packaging structure with the largecontact area of claim 31, wherein an insulation layer is deposited atthe side wall of the bottom through hole, therefore the bottom metalinterconnecting structure is electrically insulated from conductivematerial of the chip surrounding the bottom through hole through theinsulation layer.
 33. The wafer level packaging structure with the largecontact area of claim 31, wherein the bottom through hole is formed in anon-effective circuit preparing area.
 34. The wafer level packagingstructure with the large contact area of claim 31, wherein said thesemiconductor chip is a MOSFET (Metal Oxide Semiconductor Field EffectTransistor), wherein the plurality of first metal bonding pads at leastcomprise a gate electrode and a source electrode of the chip, and adrain electrode of the chip is formed at the bottom metal layer.
 35. Thewafer level packaging structure with the large contact area of claim 31,wherein a side plastic packaging layer is formed to cover a side surfaceof the chip.
 36. The wafer level packaging structure with the largecontact area of claim 31, wherein the contact bonding pad comprises pinsextending to the edge of the top packaging layer.